A joint program involving the study and practical performance of a foil-flyer electromagnetic accelerator has recently been initiated by Atomic Weapons Establishment, Aldermaston, and Loughborough University. As an initial phase of the work, both 0-D and 2-D numerical models for the foil-flyer accelerator have been developed. The 0-D model, although very crude, is capable of providing an insight into the accelerator phenomena and is currently used for parametric design studies. The 2-D model is based on the well-proven Loughborough filamentary modeling technique and is capable of accurately calculating the 2-D distribution of current, velocity, acceleration, and temperature of the flyer, together with the complete distribution of the magnetic and electric fields generated during a shot. The paper presents the two models and compares typical theoretical predictions with the corresponding experimental results.

Numerical Modelling of a Flyer Plate Electromagnetic Accelerator

This article deals with the measurement of current distribution through the rail cross section of an electromagnetic rail launcher. A measurement approach based on a loop system magnetically coupled to the launcher that is placed along the rails is proposed. The estimation of the current distribution in the rail, following the basic rules of the partial-inductance method, is discussed in this article. To test the proposed method, an experimental analysis on an “ad-hoc” -developed multiconductor rail prototype supplied by a high-voltage capacitor bank is presented. The experimental results obtained by the proposed method were compared with the direct-current measurements achieved by a set of Rogowski coils showing good agreement for different current values.

Pulsed-Current Distribution in Electromagnetic Rail Launchers

An experimental programme, leading to the development of a foil-flyer electromagnetic accelerator (FFEMA), is being conducted at AWE. A high current pulsed power generator driving a foil-flyer is used to provide tailored impulse profiles into targets for testing material properties at high strain rates. This work has required the design and construction of both an experimental platform to conduct the experiments, named AMPERE, as well as the development of a number of computer models to predict the electrical and mechanical performance of the foil-flyer and its interaction with a target.

Foil-flyer electro-magnetic accelerator initial results from a new AWE pulsed power generator

In this article, we present a novel measurement method to estimate the current distribution in electromagnetic rail launchers. A loop array is magnetically coupled with the railgun to reconstruct the current barycenter position, from which we can argue on the current distribution through the rail cross section. After describing the adopted measurement procedure, we present the results of an experimental analysis performed using the NGL60 rail launcher at the laboratories of the French-German Research Institute of Saint-Louis (ISL). We also compare the experimental results with finite-element simulations, and we show the agreement during the current pulse transient. Finally, we provide a measurement uncertainty analysis performed using Monte Carlo method.

Current Distribution in Railgun Rails Through Barycenter Filament Model

The development of both experimental and diagnostic equipment to assist with simulating the mechanical effects of cold X-ray deposition is covered by this work.

This thesis reviews the various experimental techniques suitable for conducting the electromagnetic launch of flyer plates and the chosen technique is developed into a fully functional experimental facility.

The development of a bespoke 1-dimensional computer model is also described in the text.

A novel current distribution measurement technique is also fully described. This new diagnostic approach will allow the variation of the current across the width of a large conductor to be easily determined which is something not previously demonstrated.

Electromagnetic flyer plate technology and development of a novel current distribution sensor

A joint programme involving the study and practical performance of a foil-flyer electromagnetic accelerator has recently been initiated by AWE, Aldermaston and Loughborough University.

Numerical modelling of a foil-flyer electromagnetic accelerator

A novel inductive probe, termed MIDOT, was developed for monitoring high-current flat transmission lines. While being inexpensive the probe does not require calibration, is resistant to both shock waves and temperature variations, and it is easy to manufacture and mount. It generates strong output signals that are relatively easy to interpret and has a detection region limited to a pre-defined part of the transmission line. The theoretical background related to the MIDOT probes, together with their practical implementation in both preliminary experimentation and high-current tests, is also presented in the paper. The novel probe can be used to benchmark existing 2D numerical codes used in calculating the current distribution inside the conductors of a transmission line but can also easily detect an early movement of a transmission line component. The probe can also find other applications, such as locating the position of a pulsed current flowing through a thin wire.

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MIDOT: A novel probe for monitoring high-current flat transmission lines.

Summary form only given. The work described has arisen as part of an on-going joint research programme between AWE and Loughborough University into the dynamics of electromagnetically accelerated flyer plates. A determination of the current distribution (or at least confirmation of the uniformity of the distribution) in a flat transmission line is needed in order to confirm the uniform acceleration of the flyer plate. To this end a novel mutual inductance based sensor has been developed and termed MIDOT. The sensor is calibrated using a stripline comprising an array of independent parallel filaments across the width of the transmission line with a known current flowing through each. This enabled the positional sensitivity of the sensor to be established. A subsequent series of detailed experiments confirmed that the MIDOT sensor can be used to identify accurately the currents flowing in the independent filaments under transient conditions. In contrast to previous work published on the flyer plate program, this paper is dedicated to the development of the bespoke sensor used to determine the current distribution across the flyer plate. The experimental development and results have not previously been published in great detail. The sensor has been developed to a stage where its proof of principle has been convincingly demonstrated on a low voltage test bed and it has been used to provide initial results when fielded on the high current AMPERE and QUATTRO facilities at AWE and Loughborough University respectively.

N. Graneau

Papers

Numerical Modelling of a Flyer Plate Electromagnetic Accelerator

Foil-flyer electro-magnetic accelerator initial results from a new AWE pulsed power generator

Numerical modelling of a foil-flyer electromagnetic accelerator

MIDOT: A novel probe for monitoring high-current flat transmission lines.

A bespoke non-invasive current distribution sensor for use with a flat transmission line